ON THE ARRANGEMENT OF THE FCETAL MEMBRANES IN THE CETACEA. 479 



and fitted into the intervals between those folds. They gradually subsided 

 towards the corpus uteri. In the left horn the rugse of the chorion were much 

 less strongly marked in correspondence with the feebler folds of the mucous mem- 

 brane. Except in three limited areas, the entire outer surface of the chorion was 

 thickly studded with villi. These spots, bare of villi, corresponded to the three 

 openings into the uterus, viz., the os uteri internum, and the mouths of the two 

 Fallopian tubes (fig. 13, a, b, b). The spot opposite the os internum had a stellate 



Stellate non-villous portion of the chorion of Orca opposite the os uteri. About half the size of nature. 



form ; the central space of which was nearly the size of a crown piece, and from 

 it about twelve radii extended for a short but varying distance. The radii were 

 separated from each other by folds of the chorion, thickly studded with villi, which 

 fitted between the folds of mucous membrane, already described as converging 

 to the os uteri internum.* The spots opposite the mouths of the Fallopian tubes 

 formed the poles of the chorion, and were not larger than kidney beans. They 

 were not very readily recognised, on account of the puckered rugose condition 

 of the polar portions of the chorion, and it was not until after the blood-vessels 

 of the villi had been injected with coloured gelatine that their form and appear- 

 ance were satisfactorily determined. The absence of villi on those parts of the 

 chorion, which corresponded to the uterine openings, bears obviously a special 

 relation to the absence of a mucous surface at those spots into the depressions 

 in which the villi could be received ; for though the chorion was lying loose in 

 the uterine cavity when I opened into it, there can be no doubt that, before the 

 uterine liquor had been evacuated by Mr Gatherer, the chorionic villi had been 

 lodged within the uterine crypts, as the hand and fingers fit into a glove. * 



' When I described and figured (Transactions of this Society, vol. xxvi., fig. 1 7) the only hare spot 

 which I had recognised in the chorion of the foetus of the Longniddry Balcenoptera, I regarded it, in 

 all probability, as one of the poles of the chorion, as the non-villous spot opposite the os internum 

 was not then known. The further knowledge which I have gained from the examination of this 

 Orca leads me now to thiuk, from its size and the projection of the marginal fold, that it was a 

 portion of the bare spot opposite the os uteri internum. 



VOL. XXVI. PART II. 6 I 



